This invention relates to easy opening containers or cans which may be opened by hand without benefit of an opening tool.
To date, the most commercially successful easy opening cans utilize a tab which is formed by scoring the can end panel and removed by grasping a ring attached thereto and ripping out the tab from the end panel along the score lines. Aluminum is usually utilized for a ring-tab ends of this type because its soft and malleable qualities which allow the use of substantial residual scoring depths while still permitting removal of the tab by hand.
However, aluminum can ends are objectionable from a number of standpoints. Aluminum is expensive and of relatively low strength as compared with a metal such as steel so that large quantities of aluminum must be utilized to provide can ends of sufficient gauge to withstand internal pressures generated within the cans. In addition, aluminum is expensive relative to steel, and aluminum can ends are also undesirable as compared with steel from an ecological standpoint since aluminum is not readily degradable. Furthermore, aluminum can ends are often utilized with steel can bodies and this combination is undesirable since an electrochemical reaction may be set up within the can due to its dual metallic nature, thereby creating the risk that the contents within a container may become contaminated or, at a minimum, the taste of those contents may be affected.
As a result, a good deal of emphasis has been placed of late on easy opening can designs which may utilize any metal including steel.
U.S. Pat. No. 3,871,550 -- Chiappe discloses an easy opening can end having a preformed or pre-cut dispensing opening which is sealed closed by a plastic closure member bonded or otherwise attached to one side of the dispensing opening. The closure member or tab includes an outwardly extending protuberance for engagement by the fingers during opening.
In an easy opening can end of this type, the design must achieve several important functions. First, the means of attaching the closure member must assure that the closure member remains in place. Second, the hinge associated with the closure member should have a memory so as to permit the closure member to remain in the open position during dispensing. Third, means must be provided to permit the push-in closure member to be open all the way without requiring the opener's fingers to be inserted into the container. And fourth, the closure member must be capable of being pushed in with relative ease.